1. Field of the Invention
The present invention relates, in general, to a method for the formation of device separation film among manufacture processes for a semiconductor device and, more particularly, to a method for forming a field oxide film in the semiconductor device, capable of diminishing the stress of a silicon substrate and improving the separation characteristic of the semiconductor device.
2. Description of the Prior Art
For better understanding of the background of the present invention, there will be given the description for a conventional method for forming a device separation film in a semiconductor device, with reference to FIG. 1.
As shown in FIG. 1, a silicon substrate 1 is covered with a pad oxide film 2 which is subsequently overlaid with a nitride film 3. An etching process is carried out to open predetermined portion of the nitride film 3 in which a field oxide film is to be formed, leaving a pattern of the nitride film 3.
Thereafter, another nitride film is deposited on the opened portion, so as to form a spacer film 7 at either side wall thereof. Using the spacer film 7 and the nitride film 3 as an etch mask, a trench is formed in the silicon substrate 1, to which a wet oxidation process is subsequently applied, in order to form a field oxide film (not shown in this figure).
In the conventional process for forming a field oxide film, however, there occurs a problem in that the silicon atoms in the silicon substrate are replaced with impurities since the silicon substrate is rapidly oxidized as the oxidation process is directly carried out on the silicon substrate at high temperatures. What is worse, a bird's beak comes to forms thick with the conventional method, making the surface of the field oxide film rough and increasing a leak current.